With PHP you have the phpinfo() which lists installed modules and then from there look up what they do.
Is there a way to see what packages/modules are installed to
As aaronasterling says, all .py or .pyc files on sys.path is a module because it can be imported. There are scripts that can let you find what external module is installed in site-packages.
Yolk is a Python command-line tool and library for obtaining information about packages installed by setuptools, easy_install and distutils and it can also query pypi packages.